🇫🇮 Finland Prequalification CTF 2026 — Writeups

Personal writeups for 2026.challenge.fi.

🏁 The challenge has now ended. Final results below.

Legend: ✅ Solved (flag found) · 🔄 Tried (no flag) · ❌ Not solved

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📊 Progress

Category	✅ Solved	🔄 Tried	❌ Not Solved	Total
Forensics	6	0	3	9
Misc	2	0	2	4
Cryptography	4	0	4	8
Reverse Engineering	3	0	5	8
Web Exploitation	5	1	4	10
Binary	1	0	3	4
Boot 2 Root	2	1	0	3
Total	23	2	21	46

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🔬 Forensics

Challenge	Points	Status	Writeup
alog	113	✅ DDC{Tim3_Tr4v3l_L0g_An4lys1s}	📄 Writeup
Broken Invoice	117	✅ DDC{ANOTHER_INVOICE_TO_PRINT}	📄 Writeup
Pepstein	123	✅ DDC{0h-n0-w3-607-f0und-0u7}	📄 Writeup
Persistance is Key	368	✅ DDC{M4gnific3nt-M4lwar3-R3mov4l}	📄 Writeup
Peaceful	898	✅ DDC{w000000w_d1d_y0u_4ctually_us3_v0l4t1l1ty}	📄 Writeup
SOC Nightmares	994	❌ Not solved	📄 Writeup
Windows Forensics Hell	981	❌ Not solved	📄 Writeup
Youve got mail 2!	888	❌ Not solved	📄 Writeup
Youve got mail!	908	✅ DDC{l1v1ng_0ff_th3_l4nd_1s_th3_b3st_f34l1ng_dc9ed4584956}	📄 Writeup

🎲 Misc

Challenge	Points	Status	Writeup
Hasher: Trust the Hash (They Said)	131	✅ DDC{letmeinplease}	📄 Writeup
I have lost my package	403	✅ DDC{LLM_7rick3d_m0r3_34sily_7h4n_my_gr4ndm4}	📄 Writeup
UUID Guesser	974	❌ Not solved	📄 Writeup
Relay Chat	988	❌ Not solved	📄 Writeup

🔐 Cryptography

Challenge	Points	Status	Writeup
Binary Caesar	143	✅ ddc{galois_meets_caesar}	📄 Writeup
Fibonacci Caesar	184	✅ DDC{pisano_sequence_solves_fibonacci_caesar}	📄 Writeup
The Contract	350	✅ Solved	📄 Writeup
Disk Encryption	350	✅ DDC{d1sk_3ncrypt10n_1s_w31rd}	📄 Writeup
Bad transmission	994	❌ Not solved	📄 Writeup
ECC-INIT	1000	❌ Not solved	📄 Writeup
Speedrun	484	❌ Not solved	📄 Writeup
Zero Knowledge Census Work	994	❌ Not solved	📄 Writeup

⚙️ Reverse Engineering

Challenge	Points	Status	Writeup
Unbake the cake	155	✅ DDC{lets_go_unbaking}	📄 Writeup
Call Me Maybe	190	✅ DDC{ltr4c3_my_l1br4ry_c4lls}	📄 Writeup
WiFi Heist	179	✅ DDC{y0u_cr4ck3d_th3_c0d3}	📄 Writeup
Flag Checker 3	994	❌ Not solved	📄 Writeup
Mitosis	960	❌ Not solved	📄 Writeup
Reactor	974	❌ Not solved	📄 Writeup
Stackless	981	❌ Not solved	📄 Writeup
Ziggler	994	❌ Not solved	📄 Writeup

🌐 Web Exploitation

Challenge	Points	Status	Writeup
Existential loading bar	174	✅ DDC{br0_f0rg0t_th3_s4lt}	📄 Writeup
G-Server	174	✅ DDC{str41ght_0utt4_s0urc3_c0d3}	📄 Writeup
PleaseNoCry	203	✅ DDC{N0_cry1ng_1n_7h15_h0u53}	📄 Writeup
Bootstrap Betrayal	231	✅ DDC{pwn3d_m1n10_3nvs_v4r14bl3s}	📄 Writeup
Backup	926	❌ Not solved	📄 Writeup
Content Type	994	❌ Not solved	📄 Writeup
Corsica	981	❌ Not solved	📄 Writeup
Hook Relay	974	❌ Not solved	📄 Writeup
Let me Google that for you	988	🔄 Tried	📄 Writeup
Report Error	926	✅ DDC{W0W_y0u_5ur3_r3p0rt3d_4n_3rr0r_1387ysdlkj12}	📄 Writeup

💣 Binary

Challenge	Points	Status	Writeup
fear of long words	350	✅ DDC{D3m0n1c_d1ct1on4ry_d3str0y3r}	📄 Writeup
Cactus	988	❌ Not solved	📄 Writeup
Can You Catch Me?	994	❌ Not solved	📄 Writeup
GoodVM	988	❌ Not solved	📄 Writeup

🖥️ Boot 2 Root

Challenge	Points	Status	Writeup
kopi pasta	368	✅ DDC{bruh_i_p4s73d_4_bi7_700_much}	📄 Writeup
Squeaky Clean 1	952	✅ DDC{Sql1te_To_Auth0riz3d?!}	📄 Writeup
Squeaky Clean 2	981	🔄 Tried	📄 Writeup

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🗂️ Repository Structure

📁 Binary/
📁 Boot 2 Root/
📁 Cryptography/
📁 Forensics/
📁 Misc/
📁 Reverse Engineering/
📁 Web Exploitation/

📝 Notes

• All writeups are in English.
• Minimal amount of AI was used for solving the challenges.
• Most of the writeups were copy written with AI after solving and writing the original version of the writeup. AI was used to make the writeups more concise and easier to read.
• Some writeups has also AI generated image explaining the solution in one image. Those were generated by Google Gemini 3 Pro image tool (Nano banana pro).